1. Field of the Invention
The present invention relates to an electron emission device and a display apparatus using the same, especially to a flat panel display apparatus in which a plurality of the electron emission devices are arranged in an image display array, i.e. in a matrix arrangement.
2. Description of the Related Art
Conventionally, FEDs (field emission display devices) are known as flat type light-emitting display devices having an array of cool-cathode type electron emission sources whose cathodes are not required to be heated. It is necessary to unitize the flat type display device utilizing FEDs to develop an ultra-large display unit system for a next generation. Electron emitting devices as electron emission sources of FEDs include devices having a metal-insulator-semiconductor (MIS) structure and devices having a metal-insulator-metal (MIM) structure.
As shown in FIG. 1, an electron emission device having the MIS structure has a diode structure in which a top electrode 15 that is a metal thin-film electrode on the top is at a positive potential Vd and in which a bottom electrode 11 that is an ohmic electrode on a backside substrate 10 of glass is at a ground potential. When the voltage Vd is applied between the bottom electrode 11 and top electrode 15 to inject electrons into an electron supply layer 12, electrons move in an insulator layer 13 toward the top electrode 15. Since a diode current Id flows and the insulator layer 13 has a high resistance, a major part of the applied electric field acts on the insulator layer 13. Some of electrons that have approached the top electrode 15 pass through the top electrode 15 because of the presence of the strong electric field to be emitted into the external vacuum. Electrons xe2x80x9cexe2x80x9d emitted by the top electrode 15 of the electron emission device (emission current Ie) are accelerated by a high acceleration voltage Vc applied to a collector electrode (transparent electrode) 2 provided on a front faceplate 1 in a face-to-face relationship with the same and are collected by the collector electrode 2. When the collector electrode is coated with a luminescent material 3, visible light associated with the element will be emitted.
In a matrix type flat panel display device formed in a matrix-like configuration in which top electrodes and bottom electrodes are orthogonal to each other respectively, a plurality of electron emission devices having the MIS (or MIM) structure are constructed by sequentially forming a bottom electrode, a semiconductor (or metal) electron supply layer, an insulator layer, and a top electrode on a substrate in each of regions where the top and bottom electrodes intersect each other. The top electrode is a very thin metal film to be formed as thin as possible to effectively draw out electrons from the insulator layer in view of mean free path of electrons, so that the top electrode tens is formed with a thickness of several or tens nano-meters. The thin top electrode is formed so as to straddle the precipice portions caused by the stack of the bottom electrode, the electron supply layer and the insulator layer. Thus the thickness of the top electrode at the precipice portion becomes thinner than that of the other portions. As a result, a high resistivity of the thin portion of the top electrode causes an uneven electric field to bring a drawback of destruction in the top electrode.
To overcome such a drawback, an MIM structure has been suggested in Japanese Patent Kokai No. Hei 11-120898, in which as shown in FIG. 2, the surface of the bottom electrode 11 other than the electron emitting section is covered with the insulating protective film and then the bus electrode is formed both on the insulating protective film and the backside substrate 10 in the manufacturing process.
However, the uneven electric field caused by the thin portion""s high resistivity in the top electrode still appears with a risk of breakage of the bus electrode in the case that the thickness of the stacked layers, particularly, the insulator layer is very thick, since no insulating protective film is formed on the backside substrate between the adjacent electron emitting sections.
In addition, the bus electrode directly comes in to contact with the portion of the backside substrate 10 between the adjacent electron emitting sections because such a portion is temporally exposed. After that, in the sealing step of the front-side substrate and the backside substrate, the substrates for a panel to be sealed is kept under a high temperature condition for a long time period. In such a condition, alkaline components leak from the backside substrate of glass to react with the top electrode directly contacted and then migration and electrode corrosion occur in the top electrode.
Moreover, Japanese Patent Kokai No. Hei 11-185675 discloses an electron emission device based flat panel display apparatus. This apparatus includes electron emission devices constructed in such a manner that the bus electrode is kept in direct contact with the upper thin-film metal electrode, so that the portion of the bus electrode concentrate the electric field since the bus electrode has a low resistivity in comparison with the upper thin-film metal electrode. As a result, there is a problem that reduction of the electric field to be normally supplied to the electron emitting section of the upper thin-film metal electrode.
The present invention has been conceived taking the above situation into consideration, and it is an object of the invention to provide a flat panel display device utilizing such electron emission sites capable of providing stable electron emission without deterioration.
The flat panel display device according to the invention comprises:
a backside and a front-side substrates facing each other with a vacuum space therebetween;
a plurality of electron emission sites provided on said backside substrate; each of said electron emission sites including
a bottom electrode formed on a surface of said backside substrate proximate to said vacuum space,
an insulator layer formed over said bottom electrode, and
a top electrode formed on said insulator layer and arranged individually apart from each other and facing said vacuum space;
a plurality of bus electrodes for electrically connecting the neighboring top electrodes; and
insulating protective films each provided between said bus electrode and said insulator layer and between said bus electrode and said backside substrate.
In one aspect of the flat panel display device according to the invention, each of said electron emission sites further comprises an electron supply layer made of a metal or semiconductor and formed on and between said bottom electrode and said insulator layer.
In another aspect of the flat panel display device according to the invention, the device further comprises second insulating protective films formed on said backside substrate between the neighboring electron emission sites.
In a further aspect of the flat panel display device according to the invention, the device further comprises at least one transparent collector electrode formed on a surface of said front-side substrate at the vacuum space side; and at least one luminescent layer formed on said collector electrode.
In a still further aspect of the flat panel display device according to the invention, the device further comprises at least one luminescent layer formed on a surface of said front-side substrate at the vacuum space side; and at least one collector electrode formed on said luminescent layer.
In another aspect of the flat panel display device according to the invention, said electron emission sites are arranged in an image display array corresponding to the luminescent layer.
In a further aspect of the flat panel display device according to the invention, said electron emission sites arranged in the image display array are defined and partitioned by at least matrix layer or stripe layer in a dark color or black.
In a still further aspect of the flat panel display device according to the invention, the bus electrodes and the bottom electrodes have a stripe shape respectively and are disposed perpendicular to each other.